The present invention relates to the field of geophones coupled with soil to detect seismic source energy. More particularly, the invention relates to an improved apparatus and method for coupling a geophone to soil.
Seismic operations deploy geophones along survey lines. The geophones are coupled to the soil at selected locations and detect source seismic energy reflected from subsurface geologic formations and interfaces and refracted to the surface. Movement of the surface exists along any degree of the three axes, and can be measured with three sensor geophones located in a single housing.
The effectiveness of geophone coupling to soil is essential to the accurate collection of seismic data. Three sensor geophones detect the magnitude and direction of transmitted seismic energy along different axes. Geophone orientation variations from vertical introduce significant error in measurements regarding the source direction of reflected seismic energy. Slight inclinations from vertical or from a selected compass heading can be adjusted during data processing, however additional processing time, cost and effort is required. Geophones typically integrate level indicator bubbles in the geophone case, however orientation of geophones to such bubbles requires movement of the geophone case after the case is initially planted in the soil. Such movement loosens the attachment between the geophone and soil This loose attachment creates a boundary interface between the soil and geophone which reduces coupling effectiveness and accuracy of the geophone sensed data.
Geophone sensor placement is complicated in regions having varying soil conditions. In different seismic survey regions, the soil can range from marsh to consolidated or unconsolidated soil to bedrock. The hardness of each soil condition can vary greatly within a lateral distance of several meters, thereby complicating efforts to effectively couple geophones to the soil. If the geophone is not adequately planted into the soil, flow noise from wind and moving water can adversely affect the seismic data recorded. When the geophone stakes are planted into the soil, wind and moving water exert forces against the geophone which are increased by the moment arm height of the geophone. Such environmental forces cause case flexure and resonance which generate acoustic xe2x80x9cnoisexe2x80x9d and which reduce seismic data quality and require additional data processing procedures.
Conventional three component geophones use surface mounted assemblies having spikes on the lower end of the geophone housing, and such geophone cases couple the case bottom to the soil with the sensors located above the coupling point. Lateral movement of the soil and coupled case bottom is not accurately sensed at the case upper end because of case flexure and resonance. Field personnel plant each geophone by aligning the geophone case to the proper compass heading, and by monitoring a bubble level indicator to assure the vertical orientation of the geophone case. Because conventional geophone cases are planted on the surface, field personnel must bend downward as the geophone is planted. This process is time consuming, tiring, and leads to geophone installation errors.
Various systems have been developed to plant geophones in soil. U.S. Pat. No. 4,300,220 to Goffet al. (1981) disclosed a geophone holder having a frame for supporting three geophones along principal axes of sensitivity. U.S. Pat. No. 4,838,379 to Maxwell (1989) disclosed a receptacle for receiving a geophone and for permitting the release of the geophone from the receptacle. A magnetic compass and bubble level were located one meter from:.the geophone receptacle and facilitated manual installation of the geophone. U.S. Pat. No. 5,007,031 to Erich (1991) disclosed a geophone planting tool for engaging the outer geophone case as the geophone was planted into soil. U.S. Pat. No. 5,010,531 to McNeel (1991) disclosed a geophone housing having soil anchoring spikes and a level mechanism for adjusting the spikes relative to the geophone housing. U.S. Pat. No. 5,124,956 to Rice et al. (1992) disclosed a geophone housing anchored to the soil with a bow spring or drill bit larger than the housing. U.S. Pat. No. 5,231,252 to Sansone (1993) disclosed an open seismic sensor platform having a spike for anchoring each geophone to the soil.
Other devices have been developed to anchor geophones to the seafloor or to stabilize geophones against dislocation. U.S. Pat. No. 5,142,499 to Fletcher (1992) disclosed a setting tool for releasably anchoring geophone spikes to a seafloor. U.S. Pat. No. 5,189,642 to Donoho et al. (1993) disclosed a marine seismic recorder having a ballast ring cooperating with a geophone package, and United States Patent No. 5,253,223 to Svenning et al. (1993) disclosed a marine geophone package having an electronic angle gauge together with geophones arranged in the x, y and z axes. U.S. Pat. No. 5,434,828 to Ldgan (1995) disclosed a geophone stabilizer for reducing movement of the geophone due to water currents and other environmental forces.
Other devices have been developed to expedite geophone placement in land based seismic operations. For example, U.S. Pat. No. 5,315,074 to Berquist (1994) disclosed a tractor mounted device having a push tube for planting a geophone. A vibration device was connected with a push tube to facilitate soil penetration by the geophone. Although such device is useful in unconsolidated soils, the device is limited in survey regions when the hardness and composition of the soil varies.
The accuracy of seismic data significantly depends on the proper orientation of geophone housings and on the effective coupling of such housings to local soil conditions. The efficiency of seismic operations depends on the ability to quickly and accurately deploy geophones in the desired locations. Accordingly, a need exists for improved geophone planting devices and methods for coupling geophones to soil.
The present invention provides an apparatus and method for coupling a seismic geophone to soil. The apparatus comprises a portable chassis, a frame engaged with the chassis, an orientation device engaged with the frame for selectively orienting the frame to vertical, and a hammer moveable relative to the frame to contact the soil in a vertical direction for generating a case opening suitable for insertion of the geophone, wherein the hammer is retractable from the case opening generated by the hammer.
In different embodiments of the invention, a template prevents dislocation of the soil as the hammer is retracted from the case opening. A controller can control movement of the hammer in a vertical direction, and a positioning device can identify the case opening location.
The method of the invention comprises the steps of moving a portable chassis to a selected position, operating an orientation! device engaged with a frame mounted to the chassis to selectively orient the frame to vertical, moving a hammer relative to the frame to contact the soil in a vertical direction to form a case opening suitable for insertion of the geophone, ceasing downward movement of the hammer at a selected position sufficient to form a case opening having a selected shape, and retracting the hammer from said case opening without disturbing the soil compaction.